This invention relates to electric propulsion systems, and more particularly, to an improved Hall effect electric propulsion system.
Hall effect electric propulsion systems, also referred to as Hall current thrusters and ion rocket engines, have been utilized for many years on various types of spacecraft, including commercial satellites, military satellites, and space probe applications. Once in space, the Hall current thrusters provide the propulsion necessary for orbital maneuvering and directional changes. Conventional Hall current thrusters utilize external hollow cathodes to produce an arc that ionizes a noble gas propellant within an acceleration chamber. This present technique results in long arc lengths stretching from the external hollow cathode to inside the acceleration chamber, and results in an inefficient transfer of energy to the gaseous propellant introduced into the acceleration chamber. In addition, the high electromagnetic interference (EMI) from such Hall current thrusters may interfere with the operations of the spacecraft, especially communications satellites. In this regard, ability of a communications satellite to send and receive signals may be inhibited when existing Hall current thrusters are firing.
Accordingly, it is an object of the present invention to provide a Hall effect electric propulsion system.
Yet another object of the invention is to provide a Hall effect electric propulsion system that is more energy efficient than current Hall effect electric propulsion systems.
Still another object of the invention is to provide a Hall effect electric propulsion system that results in reduced electromagnetic interference.
Another object of the invention is to provide a Hall effect electric propulsion system which minimizes erosion damage to external surfaces of the spacecraft caused by non-neutralized ions expelled from the thruster.
Another object of the invention is to provide a Hall effect electric propulsion system which minimizes erosion damage to external surfaces of the spacecraft caused by non-recombined electrons emitted from an electron generator.
The present invention achieves one or more of these objectives by providing an improved Hall effect electric propulsion system. Generally, in one aspect of the present invention, the Hall effect electric propulsion system includes a magnet (e.g., an electromagnet, permanent magnet) having an internal acceleration chamber. An aperture, or throat, formed in one end of the magnet opens into the acceleration chamber. The magnetic poles of the magnet are positioned relative to each other on opposite sides of the aperture. An ionizer located within the acceleration chamber ionizes a flow of propellant molecules introduced into the acceleration chamber. An electron generator or gun external to the magnet directs an electron beam towards a magnetic field generated by the magnet about the throat. A portion of the electrons of the electron beam become trapped in a flux of the magnetic field to form an electron cloud, which functions as a phantom cathode. A positively ionized flow of propellant molecules are accelerated (e.g., electrostatically or electromagnetically) toward and pass through the electron cloud. A large portion (e.g., greater than half) of the ionized flow of propellant molecules passing through the electron cloud become neutralized by combining with a portion of the electrons trapped within the electron cloud, producing a plurality of neutral propellant molecules having momentum to produce thrust. Of importance, locating the ionizer within the acceleration chamber reduces the size of the arc needed for ionization purposes, which in turn requires less energy and increases efficiency relative to existing Hall effect propulsion systems.
In another aspect of the invention, the Hall effect electric propulsion system includes an electromagnet having an internal acceleration chamber and an aperture formed in one end of the chamber. The magnetic poles of the electromagnet are positioned relative to each other on opposite sides of the aperture, and the opposing faces of each pole are angled outward so as to be non-parallel to each other. This produces an asymmetric magnetic field which aids in trapping electrons in the field""s fringe region. An electron gun located exterior to the acceleration chamber generates an electron beam toward the asymmetric magnetic field where some of the electrons are trapped. Other electrons not trapped would impact a sacrificial anode. The positively ionized flow of propellant molecules are accelerated towards and pass through the electron cloud. A large portion of the ionized flow of propellant molecules passing through the electron cloud become neutralized by combining with a portion of electrons trapped within the electron cloud. This produces a plurality of neutral propellant molecules having momentum to provide thrust which enhances efficiency.
In one embodiment, the internal surfaces of the acceleration chamber are coated with TEFLON(copyright). TEFLON(copyright) has the property of holding a charge. When ionized propellant molecules brush up against the TEFLON(copyright) coated internal surface area of the acceleration chamber, the TEFLON(copyright) builds up a positive charge. Beyond a certain amount of initial loss, the ionized propellant molecules can brush against the internal surfaces without losing their charge, thus improving the efficiency of the Hall effect electric propulsion system. In addition, once the positive charge is built up on the TEFLON(copyright) coated internal surfaces of the acceleration chamber, the positively charged ions are repelled by the positive charge, resulting in minimal collision and erosion by the ionized particles within the acceleration chamber itself which enhances the efficiency of the system.
In another embodiment, the acceleration chamber is divided up into segments, with each segment having its own ionizer, propellant gas supply tube, and control valve. Vectorable thrust is achieved through throttling various combinations of chamber segments.
In another embodiment, a number of individual Hall effect electric propulsion systems are arranged in a pattern forming an array. The array is then attached to a side of a spacecraft. More than one array may be attached to the spacecraft. Vectorable thrust is achieved through activating various combinations of the individual Hall effect electric propulsion systems in the array.